Internal combustion engines include exhaust control mechanisms for controlling the flow of exhaust from each combustion chamber of the engine. In most instances, these mechanisms comprise valves.
In those instances where the engine operates on a two-stroke or two-cycle principal, the valve is often of the sliding or rotating type. Generally, this type of valve does not serve to ever completely close the opening or port in the combustion chamber wall or the exhaust passage. Instead, the valve moves between a first position in which the valve does not obstruct or obstructs very little of the exhaust port, and a second position in which the valve partly obstructs the port. Because the sliding or rotating type valve can partially obstruct the exhaust passage, it can be used to control the timing of the exhaust flow, and thus the performance or running conditions of the engine.
Generally, the position of the valve is arranged to be dependent upon engine speed. Thus, a crankshaft rotation sensor or crankcase pressure sensor is typically associated with the engine for providing engine speed data to an electronic control unit. The position of the valve is then controlled in accordance with the speed of the engine. These sensors, however, may suffer from accuracy and reliability problems. In addition, they increase the cost of the engine and render it more complex.
In accordance with the present invention, there is desired an improved control arrangement for controlling an exhaust timing valve.